/* -*- tab-width: 4 -*- * * Electric(tm) VLSI Design System * * File: DisjointSet.java * * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved. * * Electric(tm) is free software; you can redistribute it and/or modify * it under the terms of the GNU Lesser General Public License as published by * the Free Software Foundation; either version 3 of the License, or * (at your option) any later version. * * Electric(tm) is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with Electric(tm); see the file COPYING. If not, write to * the Free Software Foundation, Inc., 59 Temple Place, Suite 330, * Boston, Mass 02111-1307, USA. */ package com.sun.electric.database.geometry.btree; import java.io.*; import java.util.*; /** * A <a href=http://en.wikipedia.org/wiki/Disjoint-set_data_structure>Disjoint * Set</a> data structure. This is more or less a HashSet which partitions * its contents into zero or more disjoint equivalence classes. * * XXX: ought to implement union-by-rank optimization * * @author Adam Megacz <adam.megacz@oracle.com> */ public class EquivalenceClasses<V> { private final HashMap<V,V> map = new HashMap<V,V>(); private V getRoot(V v) { V v2 = map.get(v); if (v2==null) return null; if (v2==v) return v2; v2 = getRoot(v2); map.put(v,v2); return v2; } /** add a new item, placing it in its own (singleton) equivalence class */ public void insert(V v) { if (map.get(v)!=null) return; map.put(v,v); } /** merge the equivalence classes inhabited by v1 and v2 */ public void merge(V v1, V v2) { if (map.get(v1)==null) insert(v1); if (map.get(v2)==null) insert(v2); map.put(getRoot(v1), getRoot(v2)); } /** return true if v1 and v2 inhabit the same equivalence class */ public boolean isEquivalent(V v1, V v2) { return getRoot(v1)==getRoot(v2); } }